Hydrogen sulfide is a material commonly available from many sources and potentially useful when converted to other materials such as elemental sulfur or sulfuric acid. However, recovery of hydrogen sulfide from various sources for conversion is frequently difficult or expensive. For example, in the refining of petroleum, hydrogen sulfide is produced in large quantities as an undesirable dangerous contaminant mixed with larger quantities of other materials. Often hydrogen sulfide thus produced is passed into the atmosphere as waste material, since the cost of recovery is not warranted by the value of the product recovered. However, in populated areas such disposal of hydrogen sulfide represents a nuisance, and expensive recovery methods must be employed.
In some cases hydrogen sulfide must be removed from various process streams to prevent the contamination of those streams. For example, the presence of sulfur compounds in gasoline is detrimental, since they have a suppressing effect on octane number and cause the gasoline to be corrosive, unstable and sour. In some process streams hydrogen sulfide must be removed to prevent its detrimental effect upon later employed catalysts. For example, in catalytically reforming a gasoline fraction, a net hydrogen production is realized which is at least partially recirculated to the reforming zone to saturate olefinic material and to prevent carbonization of the catalyst. It is desirable for the recycled hydrogen-containing stream to contain as little hydrogen sulfide as possible, thus preventing its undesirable effects upon the catalyst. Thus, it is often necessary and always desirable to remove hydrogen sulfide from this and similar streams. The present invention provides improved means for recovering valuable sulfur as a by-product from hydrogen sulfide, thus providing an economical and efficient means for removing hydrogen sulfide from other materials even though it is present in relatively low concentrations.
The challenge of effective and economical recovery and conversion of hydrogen sulfide from its various sources has been approached by various means in the prior art. For instance, U.S. Pat. No. 2,972,522 describes the production of sulfur from hydrogen sulfide by the absorption of gaseous hydrogen sulfide in an ammoniacal or amine solution and oxidation with oxygen in the presence of a heterogeneous catalyst such as cobalt. U.S. Pat. No. 3,097,926 describes a process for the removal of hydrogen sulfide from gas or liquid streams by washing with aqueous alkali metal hydroxides containing a cobalt salt and a chelating agent in the presence of free oxygen. Hydrogen sulfide is thus converted to elemental sulfur. In U.S. Pat. No. 2,556,836 a process is described whereby sour petroleum distillates free from hydrogen sulfide are sweetened by treatment with an alcoholic alkali metal hydroxide in the presence of a mild oxidizing agent such as oxygen. At temperatures of 60.degree. to 200.degree. F., mercaptans are converted to disulfides. Hydrogen sulfide and other acidic compounds are reported as causing the alkali metal hydroxide catalyst to quickly become depleted in activity.